It will readily be distinguished from true croup by the fact that in the one case, true croup, the attack is insidious: the patient has been sick some time, usually several days before spasm occurs; there is also fever, with usually more cough; the voice is altered before the appearance of spasm; the first seizure is slight, almost imperceptible, and the subsequent attacks become more and more severe; dyspnoea is continuous. All these facts are in marked contrast with the picture of an attack of spasm of the glottis as we have attempted to describe it. In the one case the most alarming symptoms are at the beginning. There is an explosion of morbid phenomena, each recurrence less alarming till complete convalescence is established. In the other disease the symptoms and dangers are constantly increasing in severity, till at last the spasms become as fearful as the initial seizure in laryngismus. The morbid anatomy of the two diseases is also widely different; and this difference can be recognized during life. Simple ordinary inflammation of the larynx may give rise to hoarseness and cough; the hoarseness is, however, different from that in laryngismus. There is fever, and the hyperæmia of the organ can be readily recognized. The disease is progressive, does not present its most alarming symptoms at the beginning, and spasm, if it occurs, is a late event. It is possible that spasm of the larynx might be mistaken for a foreign body in the organ. It will be remembered that the attacks of spasm usually occur at night after the child has been asleep. The history of foreign bodies in the larynx reveals what we should expect--namely, that the accident almost always occurs during the day. In a great majority of cases this history also furnishes reliable information of some substance or object which was in possession of the child, and which has disappeared. The dyspnoea is more continuous and the course and symptoms more variable. There will therefore be no great difficulty in any case, and in most cases no difficulty at all, in making a certain diagnosis as between these two conditions. In a few cases of laryngeal tumor the symptoms are very similar to those of the disease under consideration. The attacks in the case of a pedunculated tumor on the vocal cords may take place at night and may be intermittent. The rarity of this affection in children in comparison with spasm of the larynx, and the further fact that in the case of tumor there is a more continuous disturbance of respiration, make the differentiation easy. Paralysis of the adductors gives rise to more dyspnoea during sleep, but the history and laryngeal mirror make the diagnosis easy and certain.